ZigBee Light Link (ZLL) is an open standard designed for wireless control of LED lighting. LED fixtures, sensors, timers, remotes and switches built using ZLL can connect into a wireless home network without requiring a special device to coordinate. For example, the Philips Hue is a ZLL based lighting system containing a bridge controller and a number of lighting devices (e.g. LED “bulbs”), each being a node of the network. The bridge provides an interface between the network and a user device such as a smartphone, tablet or laptop, via another wireless technology such as Wi-Fi, in order to enable the user to wirelessly control the lighting from an application (“app”) running on the user device.
To make sure that consumers can easily install and add extra devices to their home lighting network, ZLL developed a commissioning mechanism which is simple for consumers and does not have a need for a coordinator. This mechanism is known as Touchlink.
Touchlink is used for the basic commissioning of a new ZLL network or adding a new node to an existing ZLL network. Taking the Philips Hue system as an example, to connect the bridge controller and multiple light bulbs into a ZLL network, a user needs to conduct two types of Touchlink operations.
FIG. 1 illustrates the process of creating a ZLL network. ZigBee is a protocol for forming mesh networks. In a mesh network, some nodes of the network can have a dual role of both relaying messages to other nodes in the network, and also being a consumer and/or source of messages sent within the network; whereas some other nodes of the mesh network may only be sources and/or consumers of messages. ZigBee refers to the former as Routers and the latter as End Devices. ZigBee also defines a state known as Factory New (FN), which means the device is un-commissioned in that it is not currently a member of any network, and that an FN flag is set in the scan requests it broadcasts in order to indicate this fact (note: a device can be in the Factory New state when indeed fresh from the factory or “out of the box”, but can also can be reset to this state). Definitions are given in ZigBee Document 11-0037-10, Apr. 5, 2012 (e.g. see section 3).
Referring to FIG. 1, a ZLL network is formed from a Factory-New (FN) initiator node 2 and a Router node 4a (usually the initiator is an End Device). In the Hue system for example, the bridge is the initiator 2 and the light bulb is the router 4a. N.B. in the case of an LED bulb, this is not strictly a bulb in the sense of a filament bulb, but rather the term “bulb” is used herein as a shorthand for a modular lighting element (i.e. a lamp) that can be fitted into a luminaire. For example this may be a retrofittable replacement for conventional filament bulb, e.g. with the same screw or bayonet fitting.
The user can invoke the Touchlink network creation operation by selecting a “discover new device” option through the smartphone app (or such like) connected to the bridge 2. As illustrated in FIG. 1, the Touchlink operation comprises the following steps.
At step 100, the initiator (in thus example the Hue bridge) 2 broadcasts a Scan Request to light bulbs in its vicinity. The range of the vicinity is application specific.
At step 110, any receiving bulb 4 replies to the Scan Request by sending a Scan Response (FIG. 1 shows one bulb 4a only by way of illustration). According to ZLL, a device (in this case a bulb) shall only respond to a received Scan Request if the RSSI (Received Signal Strength Indication) with which it received the Scan Request is above a certain application-specific threshold. Typically, ZLL requires putting the initiator 2 and the router 4a physically close to each other. Since it is practically not feasible or convenient to put the Hue bridge 2 and blubs 4 very close, the Hue system allows a larger distance between the bridge 2 and bulbs 4 by setting a lower RSSI threshold. A bulb 4 staying outside the vicinity range set by the RSSI threshold won't respond to the request and therefore can't be discovered by the initiator 2. In that case, the user needs to temporarily move the bulb 4 into the vicinity range to complete the Touchlink operation and then move it back to its installation location.
If the initiator 2 receives a Scan Response from multiple bulbs 4, the application will choose one bulb 4a for subsequent processing. Typically, the one with the highest RSSI is chosen. In the Hue system, the user chooses a bulb in the smartphone app. At step 120, the initiator 2 may get more information on the bulb 4a of interest by sending a Device Information Request before making the selection (specifically, information on what sub-devices are supported, wherein a given device such as bulb 4a may be divided into sub-devices when it has more application endpoints, for example two independent light outputs e.g. see section 7.1.2.3.2 of ZigBee Document 11-0037-10). In response to this, at step 140 the bulb 4a replies with the information in a Device Information Response message. At step 140, the initiator 2 may send an Identify Request to the bulb 4a which has been chosen as the first Router of the new network, in order to confirm that the correct physical node is being commissioned. At step 150, the initiator sends a Network Start Request to the chosen Router (bulb) 4a in order to create and start the network.
At step 160, the Router 4a creates and starts a new network, and then replies to the Network Start Request by sending a Network Start Response. If the Router is not Factory-New, it should leave its old network before creating the new network.
The initiator 2 then joins the network.
Once the network (consisting of the initiator 2 and one Router 4a) is up and running, additional bulbs 4 can be added by conducting a network-extending type Touchlink operation.
FIG. 2 illustrates the process of adding a node 4b to an existing ZLL network. The bridge 2 can add additional bulbs 4 when being requested to do so by the user (e.g. by another selection of the “discover new device” option). As shown in FIG. 2, the steps involved in this variant of the Touchlink operation are similar to the network creation scenario, with steps 200 to 240 being the same as steps 100 to 140 respectively (i.e. up to and including the Identify Request). However, instead of sending a Network Start Request to the chosen bulb 4a, at step 250 the bridge 2 sends a Network Join Request to the chosen bulb 4b, and at step 260 the bulb 4b then joins the network by responding to the bridge 2 with a Network Join Response (leaving its old network first if necessary). Not only a Router, but also an End Device can be added to an existing network using this operation.
WO 2015/078778 A1 describes commissioning in Zigbee Light Link (ZLL) networks. The proposed solution takes advantage of the existing Touchlink procedure in order to enable a controller device joining a ZLL network without having to Touchlink with every single lighting devices comprised in the ZLL network.
US 2010/150063 A1 describes a method for a new node to join an ad-hoc network. The method includes two basic functions. When the new node is allowed to join the network, the indicating device of the node being joined generates an indication. When the new node joins the network, the indicating device of the new node also generates an indication